Red eyes: common causes and what to do

Redness of the eye is an external sign of dilation of the superficial vessels of the eye. This symptom alone does not indicate a specific disease, as redness can occur with infection, allergy, inflammation, irritation, trauma, increased intraocular pressure, and some systemic diseases. Professional sources emphasize that the conjunctiva is most often involved, but redness can also be associated with damage to the cornea, uveal tract, episclera, or sclera. [1]

Clinically, it's not the presence of redness itself that's important, but its combination with other symptoms. If the eye is simply red, but there's no pain, decreased vision, photophobia, trauma, or contact lens wear, the likelihood of a serious pathology is lower. However, if the redness is accompanied by pain, blurred vision, photophobia, a foreign body sensation, pupil changes, a cloudy cornea, or significant discharge, the situation becomes fundamentally different and requires more urgent evaluation. [2]

The most common mistake is to automatically assume that any red eye is "conjunctivitis." In practice, conjunctivitis is indeed the most common cause of acute red eye, but keratitis, uveitis, scleritis, foreign body injury, chemical burn, endophthalmitis, and acute angle-closure glaucoma can all be hidden under a similar mask. Therefore, the task of the doctor and the patient is not to guess the disease based on eye color, but to recognize dangerous signs in a timely manner. [3]

Current recommendations for red eye syndrome rely not on a single symptom, but on clinical risk stratification. This involves assessing the nature of pain, visual acuity, type of discharge, presence of itching, photophobia, association with contact lenses, history of trauma, sudden onset, and whether the condition is unilateral or bilateral. This approach helps quickly differentiate conditions that often resolve spontaneously or are treated conservatively from those that can quickly lead to corneal ulceration or irreversible vision loss. [4]

It's especially important to understand that red eye isn't just an ophthalmological complaint, but also a symptom that's sometimes associated with a systemic disease. This occurs in autoimmune processes, particularly in some cases of uveitis and scleritis, as well as in severe inflammatory conditions, when eye damage becomes part of a broader underlying disease. Therefore, a comprehensive article on this topic should describe not only local manifestations but also the relationship to the patient's overall condition. [5]

What's behind the redness?	How dangerous is it usually?	Typical landmark
Conjunctivitis	Mostly harmless	Discharge, itching or burning, superficial redness
Dry eye disease	Usually harmless, but may impair quality of life	Burning, sand, intermittent fogging
Blepharitis	Usually harmless, chronic course	Redness of the eyelids, crusts on the eyelashes
Subconjunctival hemorrhage	Most often benign	A bright red spot without pain or loss of vision
Keratitis	Potentially dangerous to vision	Pain, photophobia, decreased vision, contact lenses
Anterior uveitis	Dangerous to vision if treatment is delayed	Pain, photophobia, blurred vision
Scleritis	Dangerous for vision	Deep, severe pain, sometimes associated with an autoimmune disease
Acute attack of angle-closure glaucoma	Emergency condition	Severe pain, nausea, red eye, blurred vision

The table is compiled from data from the US National Eye Institute, the Royal Children's Hospital Melbourne, the Merck Manual, and clinical sources on red eye. [6]

The main causes of eye redness

Conjunctivitis remains the most common cause of red eye. The National Eye Institute defines conjunctivitis as inflammation with redness and swelling of the inner surface of the eyelids and the white of the eye. Viral forms are the most common, easily transmitted, and often accompanied by a watery discharge. Bacterial forms often produce mucopurulent discharge and eyelid agglutination, while allergic forms cause severe itching, lacrimation, and bilateral lesions. [7]

It's especially important to distinguish allergic conjunctivitis from infectious conjunctivitis. Allergic conjunctivitis typically affects both eyes, the leading symptom is itching, and typical triggers include pollen, dust mites, mold, and animal dander. This type of conjunctivitis is not contagious, which fundamentally changes both isolation recommendations and the treatment approach. [8]

Dry eye disease is one of the most common non-infectious causes of redness. It develops when the tear film is insufficiently produced, breaks down too quickly, or functions poorly. Patients experience this as burning, dryness, scratchiness, intermittent fogging, and redness, especially after prolonged exposure to a screen, wind, air conditioning, or meibomian dysfunction. [9]

Blepharitis often combines eye redness with redness and irritation of the eyelid margins. The National Eye Institute notes that this condition causes the eyelids and eyelashes to become red, itchy, and swollen, and crusting and foamy tears may develop. While blepharitis is usually not dangerous to vision, it can contribute to chronic redness, increased dryness, and, in severe cases, corneal damage. [10]

A subconjunctival hemorrhage can be alarming because the eye becomes bright red, as if filled with blood. However, in most cases, it is a benign condition: the blood is located under the conjunctiva and does not affect the cornea or internal structures of the eye, so vision is usually not affected. This hemorrhage is often painless and can occur after coughing, vomiting, straining, mild trauma, or for no apparent reason at all. [11]

Corneal processes—keratitis, corneal ulcers, and traumatic erosions—are fundamentally more important in terms of prognosis. The National Eye Institute notes that corneal lesions are typically accompanied by pain, lacrimation, photophobia, blurred vision, and severe redness. Contact lenses play a special role: the US Centers for Disease Control and Prevention emphasizes that wearing contact lenses is associated with an increased risk of keratitis, and microbial keratitis in contact lens wearers, in severe cases, can lead to blindness or corneal transplantation. [12]

Anterior uveitis and scleritis are less common, but they often result in a combination of red eye, severe pain, and vision loss. Uveitis is characterized by pain, redness, photophobia, floaters, and blurred vision. With scleritis, the pain is typically deeper and more intense, sometimes described as boring, and the inflammation itself is considered severe and potentially destructive to ocular tissue. Episcleritis, in contrast, is usually more superficial, benign, and self-limited. [13]

An acute attack of angle-closure glaucoma is one of the most dangerous causes of red eye. The National Eye Institute explicitly classifies it as a medical emergency and recommends seeking immediate medical attention if there is a combination of intense pain, red eye, blurred vision, and nausea. Clinical guidelines also describe a cloudy cornea and a poorly reactive, moderately dilated pupil. [14]

Cause	Pain	Itching	Discharge	Vision	Special tips
Viral conjunctivitis	Usually moderate or absent	May be	Watery	Usually preserved or slightly clouded	Often bilateral, contagious
Bacterial conjunctivitis	Usually moderate or absent	Usually no	Mucopurulent	Usually saved	Gluing eyelids together in the morning
Allergic conjunctivitis	There is usually no severe pain.	Expressed	Watery	Usually saved	Both eyes, seasonality, swelling
Dry eye disease	Burning, discomfort	Sometimes	There is no typical purulent discharge	Intermittent fogging	Increased by screens and dry air
Blepharitis	Discomfort, burning	Often	Crusts on eyelashes	Usually saved	Redness of the eyelid margins
Subconjunctival hemorrhage	Usually no	No	No	Doesn't suffer	Bright red spot
Keratitis	Often expressed	Usually no	May be	Often reduced	Contact lenses, photophobia
Anterior uveitis	Expressed	No	There is usually no pus.	Often reduced	Photophobia, floaters
Scleritis	Deep strong	No	Usually no	May decrease	Autoimmune diseases, severe pain
Acute attack of angle-closure glaucoma	Very strong	No	Usually no	Reduced	Nausea, blurred vision

The table is compiled from data from the US National Eye Institute, the US Centers for Disease Control and Prevention, the Royal Children's Hospital Melbourne, the Merck Manual, and Moorfields Clinic. [15]

Symptoms and red flags

The most useful principle in assessing red eye is to look not only at the color itself, but at the symptom profile. Itching strongly suggests an allergy. Purulent discharge suggests bacterial conjunctivitis or, in more severe cases, infectious keratitis. A burning sensation and gritty sensation are typical of dry eye and blepharitis. A combination of pain, photophobia, and visual impairment requires ruling out corneal damage, uveal tract damage, or increased intraocular pressure. [16]

Photophobia is particularly important as a marker of deeper pathology. In textbooks on red eye, it is repeatedly highlighted as a sign of a potentially sight-threatening process. Photophobia, along with pain and decreased visual acuity, is characteristic of keratitis, anterior uveitis, and acute glaucoma, whereas in uncomplicated superficial conjunctivitis, it is usually absent or mildly expressed. [17]

Contact lenses deserve special attention. If a contact lens wearer complains of redness, pain, tearing, photophobia, or decreased vision, this is no longer a situation where prolonged observation at home is acceptable. The US Centers for Disease Control and Prevention emphasizes the link between contact lenses and keratitis, including microbial keratitis, and clinical guidelines classify infectious keratitis in contact lens wearers as a condition requiring urgent examination by an ophthalmologist. [18]

Trauma, chemical exposure, and the sensation of a foreign body are also considered red flags. In the case of a chemical burn, the first priority is immediate, copious irrigation rather than waiting for an examination. If a foreign body is present, especially if accompanied by pain and tearing, erosion or deeper damage to the cornea must be ruled out. The National Eye Institute and clinical guidelines emphasize that serious eye trauma and severe pain require urgent care. [19]

Particularly alarming is the combination of a red eye with nausea, vomiting, headache, and blurred vision. This combination of symptoms is typical of an acute attack of angle-closure glaucoma. This is not just a painful eye, but a true emergency, in which delay can lead to rapid and irreversible damage to the optic nerve. [20]

Benign conditions usually present differently. With subconjunctival hemorrhage, the eye may be very red, but there is no pain, pus, or vision loss. With episcleritis, there is more often a localized area of redness with mild discomfort. With blepharitis, the eyelid margins and eyelashes become prominent. Therefore, the appearance of a red eye without assessing the accompanying symptoms is insufficient for a reliable diagnosis. [21]

Sign	What does it usually mean?	Degree of urgency
Severe itching, both eyes, lacrimation	Allergic conjunctivitis	Usually as planned
Burning, dryness, intermittent fogginess	Dry eye disease	As planned
Crusts on eyelashes, redness of eyelids	Blepharitis	As planned
A bright red spot without pain or visual impairment	Subconjunctival hemorrhage	Usually as planned
Severe pain, photophobia, blurred vision	Keratitis, uveitis, scleritis	Urgently
Red eye in a contact lens wearer	Infectious keratitis, corneal ulcer	Urgently
Red eye after injury or chemical exposure	Corneal injury, burn, penetrating trauma	Immediately
Red eye, nausea, headache, blurred vision	Acute attack of angle-closure glaucoma	Immediately

The table is compiled using data from the US National Eye Institute, the US Centers for Disease Control and Prevention, the Royal Children's Hospital Melbourne, and the Merck Manual. [22]

Diagnosis and differential diagnosis

A thorough diagnosis of red eye always begins with a medical history. The doctor will determine the time of onset, whether the condition is unilateral or bilateral, the presence of pain, itching, discharge, photophobia, blurred vision, trauma, exposure to chemicals, contact lens use, and systemic diseases. This initial inquiry allows one to narrow down the causes and determine whether an immediate consultation with an ophthalmologist is necessary. [23]

The next step is to evaluate visual function. Even with seemingly "normal" conjunctivitis, decreased visual acuity alters the clinical picture and raises concerns about a corneal or intraocular process. Therefore, a vision examination is a mandatory part of the examination of any patient with red eye. In red eye guidelines, decreased visual acuity is highlighted as one of the key signs of a potentially vision-threatening condition. [24]

A slit lamp examination or other magnification helps differentiate between superficial and deeper pathologies. For dry eye disease, the tear film, eyelids, and tear stability are assessed. The National Eye Institute indicates that to diagnose dry eye disease, a physician can check the amount of tears, the rate of tear film drying, and eyelid structure. Specific tests include a slit lamp, the Schirmer test, and tear breakup time. [25]

If corneal damage is suspected, fluorescein staining is crucial. It helps identify erosions, ulcers, herpetic dendritic lesions, and other epithelial abnormalities. Clinical guidelines describe infectious keratitis as a condition characterized by pain, vision loss, intense inflammation, and corneal opacity or ulceration, often visible after staining. Therefore, patients with a red eye and severe pain should not be treated blindly based on their complaints alone. [26]

Measuring intraocular pressure and assessing the pupil are necessary when an acute attack of glaucoma is suspected. In anterior uveitis and glaucoma, pupillary response, anterior chamber depth, corneal transparency, and the presence of inflammatory signs are also important. For uveitis, the National Eye Institute recommends a comprehensive eye examination and history, while for glaucoma, urgency is determined based on the typical clinical presentation. [27]

Differential diagnosis is based on a few simple questions. Is there itching or is pain predominant? Is there pus or watery discharge? Is vision affected? Does the person wear contact lenses? Is there photophobia, trauma, or a systemic inflammatory disease? It is the combination of these signs, and not just the degree of redness, that allows us to differentiate superficial conjunctivitis from uveitis, keratitis, episcleritis, scleritis, and glaucoma. [28]

What is assessed during the inspection?	Why is this important?
Visual acuity	Decreased vision increases the likelihood of corneal or intraocular pathology
Pain and photophobia	Helps differentiate dangerous conditions from superficial conjunctivitis
Type of discharge	Watery ones are more common in viral and allergic processes, purulent ones are more common in bacterial ones
Contact lenses	Increases the risk of keratitis and corneal ulcers
Fluorescein test	Allows you to see epithelial defects and ulcerative changes
Intraocular pressure	Necessary if an acute attack of glaucoma is suspected.
Eyelids and eyelashes	Helps to recognize blepharitis and meibomian gland dysfunction
Tear film and its breakup time	Important for confirming dry eye disease

The table is compiled using data from the US National Eye Institute, the Royal Children's Hospital Melbourne and the Merck Handbook. [29]

State	What helps distinguish it from others
Viral conjunctivitis	Watery discharge, contagious, often bilateral
Bacterial conjunctivitis	Mucopurulent discharge, sticking of the eyelids
Allergic conjunctivitis	Severe itching, both eyes, allergen related
Dry eye disease	Intermittent fogging, burning, screen strain
Blepharitis	Crusts on eyelashes, chronic eyelid irritation
Subconjunctival hemorrhage	A bright spot of blood without pain or loss of vision
Keratitis	Pain, photophobia, decreased vision, contact lenses, corneal defect
Anterior uveitis	Pain, photophobia, floaters, blurred vision
Episcleritis	Mild discomfort, localized superficial redness
Scleritis	Deep, intense pain, possibly related to an autoimmune disease
Acute attack of angle-closure glaucoma	Very severe pain, nausea, cloudy cornea, decreased vision

The table is compiled using data from the US National Eye Institute, Moorfields Clinic, the Merck Manual, and clinical guidelines for red eye. [30]

Treatment

Treatment for red eyes is always cause-based. You can't simply treat "redness" without understanding its cause. Some patients only need cold compresses and artificial tears, others need antibacterial or antiviral medications, others need urgent reduction of intraocular pressure, and still others need systemic anti-inflammatory therapy. Therefore, the main task at the outset is not to choose drops at random, but to correctly identify the type of process. [31]

With viral conjunctivitis, treatment is usually symptomatic. The National Eye Institute notes that most cases resolve spontaneously, and cold compresses and artificial tears can be used at home. Antibiotics are not effective against viral conjunctivitis. However, hygiene is important, as infectious forms are easily spread through hands, towels, pillowcases, and cosmetics. [32]

In bacterial conjunctivitis, topical antibiotics can speed up symptom improvement and bacterial clearance, although many cases also resolve spontaneously. This is supported by a 2023 Cochrane review. Therefore, antibiotics are not always necessary for every patient, but may be useful in certain situations, particularly with more severe discharge, occupational and household risks of infection, or an unfavorable course. [33]

For allergic conjunctivitis, avoiding allergens, taking antiallergic medications, and rinsing the ocular surface with artificial tears are important. The National Eye Institute emphasizes that allergic conjunctivitis is not contagious, and the American Academy of Ophthalmology notes that intense itching and the bilateral nature of the lesion are particularly helpful in distinguishing it from an infection. This is important because unnecessary antibiotics do not resolve the problem of allergies. [34]

Dry eye disease is treated in stages. For mild cases, artificial tears, gels, or ointments, environmental modifications, reduced exposure to wind, smoke, and dry air, humidifiers, breaks from screen time, and adequate sleep are used. For more severe cases, cyclosporine, lifitegrast, punctal occlusion, and, less commonly, surgical correction of the eyelids if they are insufficiently adherent may be prescribed. The American Academy of Ophthalmology's current guidelines for dry eye disease were updated in 2024, and the National Eye Institute details both over-the-counter and prescription treatment options. [35]

Blepharitis requires regular eyelid hygiene. The National Eye Institute recommends daily eyelid cleansing, warm compresses, and crust removal. If necessary, the doctor will add artificial tears, antibacterial agents, or anti-inflammatory drops, and also treat any associated conditions, such as rosacea or severe meibomian dysfunction. It's important to remember that blepharitis is often chronic and does not "go away" completely, but is controlled with long-term care. [36]

Subconjunctival hemorrhage most often requires observation and explanation to the patient of the benign nature of the condition. When isolated, it usually resolves spontaneously within 1-3 weeks. A completely different approach is required for keratitis, uveitis, scleritis, chemical burns, and acute glaucoma. Infectious keratitis and uveitis require urgent examination by an ophthalmologist, while scleritis often requires systemic corticosteroids or immunosuppression. A chemical burn requires immediate irrigation, and an acute attack of angle-closure glaucoma requires emergency medication and laser treatment. [37]

Cause	The main approach to treatment
Viral conjunctivitis	Cold compresses, artificial tears, hygiene
Bacterial conjunctivitis	Observation or local antibiotics as indicated
Allergic conjunctivitis	Allergen avoidance, anti-allergy medications, artificial tears
Dry eye disease	Artificial tears, environmental correction, prescription anti-inflammatory therapy as needed
Blepharitis	Eyelid hygiene, warm compresses, sometimes antibiotics or steroid drops
Subconjunctival hemorrhage	Observation and explanation if there is no injury or loss of vision
Infectious keratitis	Emergency ophthalmological care, etiotropic therapy
Anterior uveitis	Urgent ophthalmological care, anti-inflammatory treatment
Scleritis	Urgent evaluation, often systemic therapy
Acute attack of angle-closure glaucoma	Urgent reduction of intraocular pressure and subsequent specialized treatment

The table is compiled from data from the US National Eye Institute, the Cochrane review, the US Centers for Disease Control and Prevention, the Royal Children's Hospital Melbourne, and the Merck Handbook. [38]

Prevention and prognosis

Prevention depends on the cause, but there are several universal rules. For infectious conjunctivitis, hand washing and avoiding sharing towels, pillowcases, and cosmetics are essential. For contact lens wearers, the most important thing is to strictly adhere to replacement schedules, cleaning, storage, and disinfection rules, and not wear lenses longer than recommended. Lens hygiene remains one of the most important ways to prevent keratitis. [39]

Environmental modifications and visual habits are important for reducing the symptoms of dry eye disease. The National Eye Institute recommends avoiding smoke, wind, and strong air conditioning, using a humidifier, limiting continuous screen time, taking breaks, wearing protective eyewear outdoors, drinking plenty of water, and getting enough sleep. These measures are not a substitute for treatment, but in many patients, they significantly reduce redness, burning, and visual discomfort. [40]

Blepharitis prevention relies heavily on regular eyelid hygiene, especially in people with recurrent crusting, oily skin, dandruff, or rosacea. If you're prone to chronic inflammation, eyelid margin care can reduce the frequency of flare-ups and secondary dry eye. In this sense, blepharitis is more of a chronic, manageable condition than a one-time infection. [41]

To prevent traumatic and chemical causes of red eye, eye protection is essential. The National Eye Institute recommends protective eyewear when working with tools, chemicals, sports equipment, and during housework or gardening. If a chemical comes into contact with the eye, immediate rinsing is crucial, as the length of time the chemical is in contact with the eye tissue determines the severity of the injury. [42]

The prognosis for red eye varies greatly. Viral conjunctivitis, blepharitis, dry eye, and subconjunctival hemorrhage are generally favorable, although some conditions tend to be chronic or recurrent. The outcome of keratitis, uveitis, scleritis, and acute angle-closure glaucoma depends on the speed of recognition and treatment. The sooner the cause is addressed, the higher the chance of preserving vision without lasting consequences. [43]

Risk group	What is especially important
Contact lens wearers	Proper cleaning, storage and timely replacement of lenses
People with allergies	Allergen control and timely anti-allergic therapy
People with dry air and screen load	Breaks, air humidification, artificial tears
Patients with blepharitis, rosacea, dandruff	Regular eyelid hygiene
Workers at risk of injury and chemical exposure	Safety glasses and first aid training
Patients with autoimmune diseases	Fast treatment for pain, photophobia and new red eye

The table is compiled using data from the US National Eye Institute, the US Centers for Disease Control and Prevention, Moorfields Clinic, and the Merck Handbook. [44]

FAQ

Does red eyes always indicate an infection?
No. Red eyes can be associated not only with viral or bacterial conjunctivitis, but also with allergies, dry eye disease, blepharitis, subconjunctival hemorrhage, keratitis, uveitis, scleritis, trauma, and an acute attack of angle-closure glaucoma. This is why the same external symptom requires different treatments. [45]

When can red eye be monitored at home, and when should you urgently seek medical attention?
Home monitoring is only appropriate for mild symptoms without pain, without decreased vision, without photophobia, without injury, and without contact lenses. Urgent medical attention is required in cases of severe pain, photophobia, decreased vision, chemical exposure, injury, red eye in contact lens wearers, or when red eye is accompanied by nausea and headache. [46]

Can antibiotics be used for any red eye?
No. Antibiotics do not help with viral conjunctivitis and do not resolve allergies or dry eye. According to Cochrane, topical antibiotics may speed up improvement in acute bacterial conjunctivitis, but this does not mean that every patient with red eye needs them. [47]

What are the dangers of contact lenses for red eyes?
Contact lenses increase the risk of keratitis, including microbial keratitis. In contact lens wearers, a serious corneal infection can lead to vision loss or the need for a corneal transplant, so a red, painful eye with contact lenses should not be dismissed as simple conjunctivitis until keratitis is ruled out. [48]

Why does a subconjunctival hemorrhage cause the eye to be very red, but vision is not affected?
Because the blood is located under the conjunctiva, not inside the eye. The cornea and internal structures are not involved, so with an isolated case, vision usually remains normal, and the condition often resolves on its own. [49]

What most often distinguishes allergic conjunctivitis from infectious conjunctivitis?
The most useful indicator is itching. With allergic conjunctivitis, it is usually severe, often affecting both eyes, and is associated with allergens and is not contagious. With infectious forms, itching is usually a less prominent symptom, while with bacterial conjunctivitis, mucopurulent discharge is more often noticeable. [50]

Do artificial tears only help with dry eye disease?
No. Artificial tears are useful not only for dry eye disease, but also as symptomatic support for mild viral conjunctivitis, allergic irritation, and blepharitis. They reduce dryness, burning, and discomfort, although they do not replace treatment of the underlying cause if the condition is more severe. [51]

Which red eye is considered the most dangerous?
The most dangerous variants are those associated with pain, photophobia, visual impairment, a cloudy cornea, trauma, chemical damage, or systemic symptoms. In practical terms, infectious keratitis, anterior uveitis, scleritis, and an acute attack of angle-closure glaucoma are particularly dangerous. [52]